A "milsim" should be long enough to achieve the goals of the scenario Designer. I have found that creating a scenario with defined Missions with discrete time limitations written in permits participants to better manage their energy.

At the just past Operation Woodsman, I had written a 36 hour scenario with 8 discrete Missions. Each Faction , ( there were three, Allied forces , German Forces , Partisans ) had their own missions and Objectives and Timings . Missions were 3-5 hours in duration and had forced rest periods of 2-4 hours between missions. I had no one drop out.

In my opinion this format works very well, it was also employed at our D-Day event organised by Leccas .. and worked very well , That event was 24 hours duration, no one dropped out.

It is a lot more preparation work, Written mission orders have to be prepared in advance. You can also prepare alternate missions depending on the outcome of previous missions.

This format in my opinion creates a context and structure that ensures that units remain cohesive and focused on task. It also prevents events from devolving into an interminable skirmish over the same ground.